The present invention relates to heat transfer element baskets and, more specifically, to an assembly of heat absorbent plates in a basket for use in a heat exchanger wherein heat is transferred by means of the plates from a hot heat exchange fluid to a cold heat exchange fluid. The present invention has particular application in heat transfer apparatus of the rotary regenerative type wherein the heat transfer element is heated by contact with a hot gaseous heat exchange fluid and thereafter brought in contact with a cool gaseous heat exchange fluid to which the heat transfer element gives up its heat.
One type of heat exchange apparatus commonly used for gas-to-gas heat exchange in the process industry and for gas-to-air heat exchange on utility steam generators is the well-known rotary regenerative heat exchanger. Typically, a rotary regenerative heat exchanger has a cylindrical rotor divided into compartments in which are disposed a mass of heat transfer element which, as the rotor turns, is alternately exposed to a stream of heating gas and then upon rotation of the rotor to a stream of cooler air or other gaseous fluid to be heated. The heat absorbent mass typically comprises a plurality of heat transfer element basket assemblies mounted in sector shaped compartments. Each of the heat transfer element basket assemblies houses a plurality of heat transfer plates which when exposed to the heating gas absorb heat therefrom and then when exposed to the cool air or other gaseous fluid to be heated, the heat absorbed from the heating gas by the heat transfer plates is transferred to the cooler gas.
Typically, such an element basket assembly comprises a pair of spaced end plates held together by paired side straps interconnecting the end plates along the sides thereof such as shown in U.S. Pat. Nos. 3,314,472, 4,561,492 and 4,606,400. A plurality of heat transfer plates are stacked in closely spaced relationship within the basket housing to provide a plurality of passageways between adjacent plates through which the heat exchange fluids pass. The side straps which interconnect the spaced end plates extend in pairs along the opposite sides of the stacked array of heat exchange elements. On each side of the heat exchange element is a first side strap extending between the upper regions of the spaced end plates and a second side strap extending between the lower region of the end plates in spaced, parallel relationship to the first side strap. The side straps may be flanged inwardly along the longitudinal edge lying at the edge of the basket assembly to provide a retaining surface for preventing the heat transfer plates from falling out of the open ends of the element basket as shown in U.S. Pat. No. 3,314,472.
Preferably, one or more retaining bars are welded between the end plates across the top and bottom ends thereof to further assist in keeping the heat transfer element plates from falling out of the open ends of the element basket. The retaining bars may merely be disposed to lie across the top and bottom edges of the heat transfer element plates as shown in U.S. Pat. No. 4,561,492. Alternatively, in order to provide a shorter basket for a given plate height, the retaining bars may be disposed within recesses cut in the top and bottom edges of the heat transfer element plates as shown in U.S. Pat. No. 4,606,400.
The retaining bars also serve as structural members for supporting lifting means to facilitate handling of the assembled element baskets and, in particular, to facilitate the installation and removal of the element baskets from the heat exchanger. Typically, the lifting means comprises a pair of spaced aparted holes formed in a centrally located retaining bar as shown in U.S. Pat. No. 4,552,204, or a pair of spaced aparted pins integral with and passing through a centrally located retaining bar as shown in U.S. Pat. No. 4,557,318. When the lifting means comprises a pair of holes as in the aforementioned U.S. Pat. No. 4,552,204, the element basket is lifted by means of a pair of clevis means which are disposed to spa the central retaining bar about each lifting hole. Each clevis is engaged to the retaining bar by a pin which is passed through the lifting hole and each side of the clevis spanning the bar. When the lifting means comprises a pair of lifting pins as in the aforementioned U.S. Pat. No. 4,557,318, the element basket is lifted by means of a pair of lifting lugs which simply grasp the pins extending through the central retaining bar.
An element basket characterized by its compactness relative to the height element carried therein, known as the Low Profile element basket, is disclosed in commonly assigned, co-pending patent application Ser. No. 84,063, filed Aug. 11, 1987. The element basket assembly disclosed therein comprises a plurality of heat transfer element plates disposed in a stacked array between spaced end plates located at opposite ends of the stacked array of heat transfer element plates and interconnected by spaced upper and lower side straps welded to and extending between the side of the end plates at the upper and lower lateral edges thereof. A stiffening member is disposed within the stacked array of heat transfer element plates to extend transversely across the element basket assembly to interconnect the upper side straps together and to interconnect the lower side straps together thereby providing a structural cross-link between the respective upper and lower side straps whereby the structural integrity of the frame of the element basket assembly is improved. Typically, the stiffening member comprises a single plate-like member disposed within the stacked array of heat transfer plates at or near the mid-span between the end plates of the element basket with the plate-like stiffening member extending from top to bottom and side to side across the cross-section of the element basket assembly. However, the stiffening member may take other forms as discussed in the aforementioned patent application.
As disclosed in the aforementioned commonly-assigned application Ser. No. 84,063, lifting of the compact basket assembly may be facilitated by providing lifting holes in the upper region of the stiffening member for the insertion of a lifting clevis in the manner disclosed in commonly-assigned U.S. Pat. No. 4,552,204. It is an object of the present invention to provide an improved compact element basket assembly having integral lifting means which more readily facilitates handling of the assembled baskets.